Capacitors

[Superman541]

Forgive me. I need you to verify and/or clarify what I think I know about capacitors and how to choose them. Here is what I think I know:

They store and release an electric charge. Their ability to do this is capacitance. Measured in microfarads - uf.

They also have voltage and tolerance ratings, which should be printed on the body of the capacitor.

I may decide to replace some capacitors and perhaps other parts in my new Pilot 690A, which is discussed in a nearby thread, and I will have specific questions about that unit, in that thread. In the meantime, I am hoping to get clear on how to assemble a list of caps I need. For this, I may need to look at each capacitor and jot down the voltage, capacitance and tolerance ratings. I should make sure the capacitor I get is rated for no less voltage than the capacitor I am replacing. I think the tolerance should also at least match or exceed the capacitor I am replacing (percentage tolerance should be as low or lower than the cap I am replacing). Finally, the capacitance should be about the same, but not necessarily matching. A little higher capacitance rating is often acceptable.

Do I have this right?

Another question: There are different TYPES of capacitors. Electrolytics are different from others. Right? Some capacitors in a given amp have more effect on sound than others. Some audio guys choose specific brands and types of capacitors because of their performance. Two caps with identical ratings might still perform differently. Do I have that right?

 

[zackthedog]

You're very close. Capacitors in the power supply store and release voltage to smooth out the ripples in rectified DC. Coupling capacitors between tube stages block DC voltage from the power supply and allow the AC signal to pass through. They have other uses, such as tuning frequency response.

Yes, replacement capacitors should have at least a voltage rating of those you are replacing. Higher doesn't hurt because a lot of vintage equipment was designed for economy and higher voltage ratings will give you a little more assurance of safe operation. This is often very true of coupling capacitors.

Power supply capacitors are generally electrolytic, though they can be replaced by film capacitors. Electrolytic capacitors are polarized so it's important to orient them properly according to the schematic. Coupling capacitors are always film caps and these are non-polar, or bi-directional.

In the power supply you can sometimes increase the capacitance, but in my book it's usually best to stay as close to the original design as possible. Coupling capacitors should be replaced with the exact values (or as close as possible) because they help to determine the frequency poles of the amp and you can cause problems by messing with the values.

As for selection, that's a bit of a rabbit hole. There are well-made replacement parts for vintage components, like CDE can capacitors and quality coupling caps, sold by many radio and ampflifier supply houses. Now, when I rebuilt my Heathkit monoblocks, I used my preferred Mundorf electrolytics and film caps, because I think they sound better than stock replacement parts. But 1) that's years of DIY experience telling me what makes a difference in my system, and 2) I'm not concerned with the original appearance. For your project, I would stick to recommended replacement parts, otherwise you'll go nuts trying to sort out all the "boutique" brands and the accompanying debate about what's snake-oil and what isn't. That's my .02.

 

[Superman541]

Thank you! This is very helpful.

I promise not to start a thread about cables.

 

[gadget73]

With voltages, film caps don't really care if you go overboard. Replacing a 200v part with a 630v part isn't an issue. Personally I don't buy anything but 630v film caps just because it makes stocking easy and they will work basically anywhere.

With electrolytics thats not necessarily true. A 50v part replaced with a 450v part long term may not survive well. I don't know the physics of it but something about how the oxide layer on the aluminum builds up, if you run a cap grossly below rating it essentially de-rates itself and becomes a low voltage part. It also ends up with higher than normal ESR. You can go higher in voltage but I wouldn't go more than double the original. Its more expensive, larger, and doesn't offer any performance benefit.

and yeah cap selection is an endless rabbit hole. I run boring basic Illinois yellow caps in everything because they aren't expensive, they fit, and they work well. I'm sure someone out there in audio land is just screaming at the notion of using caps that cost under a buck a piece.

 

[zackthedog]

Thank you! This is very helpful.

I promise not to start a thread about cables.

Good idea. ;-) Seriously, quality generic parts will not disappoint.

 

[zackthedog]

With voltages, film caps don't really care if you go overboard. Replacing a 200v part with a 630v part isn't an issue. Personally I don't buy anything but 630v film caps just because it makes stocking easy and they will work basically anywhere.

With electrolytics thats not necessarily true. A 50v part replaced with a 450v part long term may not survive well. I don't know the physics of it but something about how the oxide layer on the aluminum builds up, if you run a cap grossly below rating it essentially de-rates itself and becomes a low voltage part. It also ends up with higher than normal ESR. You can go higher in voltage but I wouldn't go more than double the original. Its more expensive, larger, and doesn't offer any performance benefit.

and yeah cap selection is an endless rabbit hole. I run boring basic Illinois yellow caps in everything because they aren't expensive, they fit, and they work well. I'm sure someone out there in audio land is just screaming at the notion of using caps that cost under a buck a piece.

That's a good point about electrolytics, Gadget.

 

[stanko]

You're very close. Capacitors in the power supply store and release voltage to smooth out the ripples in rectified DC. Coupling capacitors between tube stages block DC voltage from the power supply and allow the AC signal to pass through. They have other uses, such as tuning frequency response.

Yes, replacement capacitors should have at least a voltage rating of those you are replacing. Higher doesn't hurt because a lot of vintage equipment was designed for economy and higher voltage ratings will give you a little more assurance of safe operation. This is often very true of coupling capacitors.

Power supply capacitors are generally electrolytic, though they can be replaced by film capacitors. Electrolytic capacitors are polarized so it's important to orient them properly according to the schematic. Coupling capacitors are always film caps and these are non-polar, or bi-directional.

In the power supply you can sometimes increase the capacitance, but in my book it's usually best to stay as close to the original design as possible. Coupling capacitors should be replaced with the exact values (or as close as possible) because they help to determine the frequency poles of the amp and you can cause problems by messing with the values.

As for selection, that's a bit of a rabbit hole. There are well-made replacement parts for vintage components, like CDE can capacitors and quality coupling caps, sold by many radio and ampflifier supply houses. Now, when I rebuilt my Heathkit monoblocks, I used my preferred Mundorf electrolytics and film caps, because I think they sound better than stock replacement parts. But 1) that's years of DIY experience telling me what makes a difference in my system, and 2) I'm not concerned with the original appearance. For your project, I would stick to recommended replacement parts, otherwise you'll go nuts trying to sort out all the "boutique" brands and the accompanying debate about what's snake-oil and what isn't. That's my .02.

A slight addition to what's been said before. In voltage doubling supplies the doubling capacitors are not smoothing out ripple, they are charging and discharging to double the voltage input to the supply. Voltage doubling supplies are common in vintage equipment.

 

[gadget73]

good point. After the doubler you'll find a smoothing cap that runs across the entire supply from + to -. The caps in the doubler see 1/2 the voltage. The upper one has it's - point at 1/2 B+ too, which is why you'll sometimes find cardboard insulated capacitors in a supply. Watch replacing those with modern. Even if the case isn't directly tied to the - terminal you'll see a fair bit of leakage to the can and you can easily give yourself a nasty shock if you touch it. Found that out the hard way with my big Bogen amps. The top of the doubler cap was sitting at +350vdc. It did not feel good.

 

[HPMguy]

Modern electrolytic caps, provided they are from a good manufacturer, are better than the ones in vintage equipment were new by most measures. Should work better even if plain general purpose if they are from Panasonic, Nichicon, or any other major supplier. Avoid cheap caps from generic Chinese sources as they are often low quality and may be at the very edge of acceptable rating tolerance, and outside of some of the larger caps, only a couple cents cheaper (I've found it's cheaper to buy ten of the smaller caps at a time, for less than a buck extra I get a decent supply of them). A lot of vintage equipment ran the filter caps near their voltage rating (49V on a 50V cap, for instance, in my KA-80) and I think one step up is a good plan. I'm only replacing a dozen or two, not building millions of amplifiers so cost is a minor consideration. A penny each over 10 million parts is a pile of dough!

There are many different specifications for capacitors, but other than specifically low leakage caps in a few places and non-polar electrolytics in a few specifics place in audio equipment, Nichicon audio grade will work fine. Modern caps are usually much smaller than vintage ones so a one step up in voltage rating will not cause problems in fit. However, film caps are usually significantly larger that electrolytic caps, and long leads with the capacitor floating up in the air is an invitation to inductance induced noise problems (hum, stray electromagnetic noise, RF interference). Keep them flat on the board or don't use them. Very high voltage ratings do NOT mean they are better capacitors, and they may not fit. Not many film caps rated a 10 or 16V either so far as I've found.

You can dig through the schematic and the specs for the originals and find "perfect" matches for the circuit requirements, but I suspect for the vast majority of people it will be wasted expense and effort as you won't hear a difference.

Most 80's and on stolid state A/B amps are direct coupled and only have coupling caps between the phono pre-amp and the pre-amp stages, usually fairly low uF rating. A film cap may or may not fit there as a 2.2uF 10V electrolytic is pretty small and a similar rating film cap (if you can find one less than 100V rating) will not.

If you have one of those amps that tends to run warm, I'd get 105C rated caps, they will last longer. My KA-900 runs very warm in the phono and pre-amp stages, so I got all 105C caps for it. Not that I expect to be worried in another 40 years about the capacitors in it....

Tube equipment is a different story, the voltages are much higher and there are always coupling caps that must be low leakage (they have to filter 300V plus DC from the AC audio signal). Film caps in that rating tend to be quite large, but they do not explode when over-stressed nearly so much....

 

[Mr Boochie]

With voltages, film caps don't really care if you go overboard. Replacing a 200v part with a 630v part isn't an issue. Personally I don't buy anything but 630v film caps just because it makes stocking easy and they will work basically anywhere.

I also like using OEM or higher voltage rated coupling caps. They are built to handle those high voltages being applied to the anode plate side.

Not sure about bypass caps. I've always replaced 25VDC rated ones (in vintage tube units) with 50VDC ones. Because of the higher outlet voltages of most of today's homes.

 

[HPMguy]

Higher line voltage makes a difference too -- if a cap is rated very near the actual voltage and the mains supply goes up a few volts, the cap is no longer adequate.

 

[dbonin]

Other than the obvious leads on the caps, Metallized Polyester Film Capacitors come in different packages.
Compare these
ECQ-E6104KF (Panasonic Film Capacitors 630VDC 0.1uF 10% MPET)

versus
104MWR630K (Illinois Film Capacitors 0.1uF 630V 10%)

I have a boat load of the yellow axials, but the Panasonic version is 50% cheaper, and I can definitively make the leads work in the recap I'm doing. Other than aesthetics or physical shape, is there a reason to avoid the orange dips? I can't see a reason to pay double unless there is a performance diff. Am I missing something?

 

[Tom Bavis]

Radial lead parts are fine if they fit. Panasonic makes good caps. The axials often have longer leads, which you need sometimes.

 

[gadget73]

physical fitment is my usual problem with them. If they fit, they'll work just fine. I have actually used them myself.

 

[dbonin]

Thanks, Tom and gadget73! I'm going to order a bunch of the cheaper panasonic ECQ-E6104KF in my next order. Hard to beat!